The central nervous system is a vital part of the human physiology that coordinates human activity. It is primarily made up of the brain and the spinal chord. The spinal chord is made up of a bundle of nerve tissue which originates in the brain and branches out to various parts of the body, acting as a conduit to communicate neuronal signals from the brain to the rest of the body, including motor control and sensations. Protecting the spinal chord is the spinal, or vertebral, column. Anatomically, the spinal column is made up of several regions, including the cervical, thoracic, lumbar and sacral regions. The cervical spine is made up of seven vertebrae and functions to support the weight of the head. The thoracic spine is made up of 12 vertebrae and functions to protect the organs located within the chest. Five vertebrae make up the lumbar spine. The lumbar spine contains the largest vertebra and functions as the main weight bearing portion of the spine. Located at the base of the spine is the five fused vertebrae known as the sacrum. The coccyx sits at the base of the spinal column and consists of four fused vertebrae.
Each of the vertebrae associated with the various spinal chord regions are made up of a vertebral body, a posterior arch, and transverse processes. The vertebral body, often described as having a drum-like shape, is designed to bear weight and withstand compression or loading. In between the vertebral bodies is the intervertebral disc. The intervertebral disc is filled with a soft, gelatinous-like substance which helps cushion the spine against various movements and can be the source of various diseases. The posterior arch of the vertebrae is made up of the lamina, pedicles and facet joints. Transverse processes extend outwardly from the vertebrae and provide the means for muscle and ligament attachment, which aid in movement and stabilization of the vertebra.
While most people have fully functional spinal chords, it is not uncommon for individuals to suffer some type of spinal ailment, including spondylolisthesis, scoliosis, or spinal fractures. One of the more common disorders associated with the spinal chord is damage to the spinal discs. Damage to the discs results from physical injury, disease, genetic disposition, or as part of the natural aging process. Disc damage often results in intervertebral spacing not being maintained, causing pinching of exiting nerve roots between the discs, resulting in pain. For example, disc herniation is a condition in which the disc substance bulges from the disc space between the two vertebrae bodies. It is the bulging of the disc material which causes impingement on the nerves, manifesting in pain to the patient. For most patients, rest and administration of pain and anti-inflammatory medications alleviates the problem. However, in severe cases, cases which have developed into spinal instability or severe disc degeneration, the damaged disc material between the vertebral bodies is removed and replaced with spinal stabilization implants. Restoration to the normal height allows the pressure on the nerve roots to be relieved.
There are many different approaches taken to alleviate or minimize severe spinal disorders. One surgical procedure commonly used is a spinal fusion technique. Several surgical approaches have been developed over the years, and include the Posterior Lumbar Interbody Fusion (PLIF) procedure which utilizes a posterior approach to access the patient's vertebrae or disc space, the Transforaminal Lumbar Interbody Fusion (TLIF) procedure which utilizes a posterior and lateral approach to access the patient's vertebrae or disc space, and the Anterior Lumbar Interbody Fusion (ALIF) which utilizes an anterior approach to access the patient's vertebrae or disc space. Using any of these surgical procedures, the patient undergoes spinal fusion surgery in which two or more vertebrae are linked or fused together through the use of a bone spacing device and/or use of bone grafts. The resulting surgery eliminates any movement between the spinal sections which have been fused together.
In addition to the spinal implants or use of bone grafts, spinal fusion surgery often utilizes spinal instrumentation or surgical hardware, such as pedicle screws, plates, or spinal rods. Once the spinal spacers and/or bone grafts have been inserted, a surgeon places the pedicle screws into a portion of the spinal vertebrae and attaches either rods or plates to the screws as a means for stabilization while the bones fuse. Currently available systems for inserting the rods into pedicle screws can be difficult, particularly in light of the fact that surgeons installing these rods often work in narrow surgical fields. Moreover, since patients can vary with respect to their internal anatomy resulting in varying curvatures of the spine, a surgeon may not always have a linear path or may have anatomical structures that must be maneuvered around in order to properly insert the surgical rods into the pedicle screw assemblies. In addition to requiring surgical skill, difficulty in placing the rods correctly into the pedicle screws can result in unnecessary increases in the time it takes a surgeon to complete the surgical procedure. Prolonged surgery times increase the risk to the patient. More importantly, improperly aligning the rods and pedicle screw assemblies often results in complications for the patient and requires corrective surgical procedures.
There exists, therefore, a need for an improved bone fixation rod and bone fixation implantation instrument that can be used by a surgeon to easily and safely insert the bone fixation rod to a plurality of embers of a bone fixation system, such as pedicle screws which have been inserted into various bone structures.